jrkob, that was an outstanding answer! I think it allays a lot of the fears my friend has. Although I still can't say for sure whether the overtaking maneuver was legal or not (whether by the literal text of the road code, or by a subjective interpretation of "driving to the conditions" - in this case a congested road with limited visibility), my friend is just going to offer a guilty plea, considering that a criminal record is not likely.
Anyway, she's in court for the summons tomorrow, so I'll update you later. Thanks again for the outstanding response from everyone.